Cost of Olympic stadium and swim centre doubles

The bill for the aquatics centre is set to double to £150 million while the budget for the stadium will rise from £280million to £500 million.

Balfour Beatty is the only remaining bidder to build the aquatics centre after two shortlisted rivals withdrew.

German firm Hochtief said it had too much other work while French company Eiffel was unhappy with a tough bidding system designed to avoid a repeat of the fiasco over the rising cost of Wembley Stadium. Balfour Beatty, a shareholder in doomed Tube maintenance firm Metronet, recently posted half-year losses of £52 million.

The Olympics Delivery Authority has been forced to admit it has no realistic hope of keeping to the £75 million cost in London's official bid book, as a result of inflation, VAT and the fact the budget was set at 2004 rather than 2012 prices.

Similar pressures have driven the main stadium's cost to £500million. It also has only one contractor lined up - Team McAlpine, the consortium responsible for Arsenal's Emirates stadium - after others failed to meet the bid criteria.

Some £9.3 billion of public and Lottery cash has been earmarked for 2012.

Next week the ODA's new chairman, John Armitt, makes his first public appearance before the London Assembly.

Lib-Dem culture spokeswoman Dee Doocey said: "This is yet more evidence to show that the original estimates were made on the back of a fag packet. I look forward to quizzing John Armitt."

The aquatics centre, which should have been completed next year, is now set to open for test events in 2011. It will include two 50m pools and a diving pool.

It will also host synchronised swimming, water polo and elements of the modern pentathlon during the Olympics.

The ODA is said to be relaxed over Balfour Beatty being the only bidder in spite of the "challenging timetable".

Howard Shiplee, its director of construction, said: "We remain confident we will appoint a world class construction company."